For me it's perfectly ok... I don't remember the exact traces, but some
sporadical SKAS-related Oops were reported... in no case they were repeatable
(since -V1 at least), so they were likely very thin races conditions.
I'm going to merge also the patches for PTRACE_SYSEMU_SINGLESTEP in SKAS,
since I'm now at releasing SKAS updates.
I'm also going to add this patch, which fixes another potential problem:
diff -puN arch/i386/kernel/ptrace.c~skas-add-wmb-for-mm-switch
arch/i386/kernel/ptrace.c
--- vanilla-linux-2.6.9/arch/i386/kernel/ptrace.c~skas-add-wmb-for-mm-switch
2005-01-26 20:12:14.233441416 +0100
+++ vanilla-linux-2.6.9-paolo/arch/i386/kernel/ptrace.c 2005-01-26
20:28:00.902525840 +0100
@@ -570,8 +570,10 @@ asmlinkage int sys_ptrace(long request,
}
atomic_inc(&new->mm_users);
+ task_lock(child);
child->mm = new;
child->active_mm = new;
+ task_unlock(child);
mmput(old);
ret = 0;
break;
/*
* Protects ->fs, ->files, ->mm, ->ptrace, ->group_info, ->comm and
* synchronises with wait4().
*
* Nests both inside and outside of read_lock(&tasklist_lock).
* It must not be nested with write_lock_irq(&tasklist_lock),
* neither inside nor outside.
*/
static inline void task_lock(struct task_struct *p)
{
spin_lock(&p->alloc_lock);
}
The release will wait at least a couple of days, since I'm adding all this
stuff... especially, since there is a lock addition, I'd like at least one
positive report from one SMP user before *officially* releasing.
I've not seen any update to them from their original version (i.e. when they
were first discussed). Is this correct?
And my doubts about their technical merit were totally wrong. I simply was
missing that SYSEMU stands to SYSEMU_SINGLESTEP as SYSCALL stands on
SINGLESTEP (in correct, >=2.6.9 kernels), while I thought SYSEMU_SINGLESTEP
was equal to the correct SINGLESTEP (I was maybe misguided by the "using it
to check the host kernel correctness" hack we need to use).
--
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade
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